Refraction is the bending of light rays as they pass from one
medium into another medium of different optical density.
The index of refraction of a transparent medium is a ratio of the
speed of light in a vacuum to the speed of light in the medium:
n = c/v where n = is the index of refraction (no units)
c = 3 x 108 m/s
v = speed of light in the medium (in m/s)
ÄNote: The greater the index of refraction of a medium,
the slower light travels in that medium.
The index of refraction: for a vacuum is one (1),
for water it is 1.33,
for diamond it is 2.42, etc.